My understanding is that these are all equivalent, in forms that get successively more colloquial. The effect of the double negative is to say that I "mustn't not go" to the bank. Hence I must go there. And yes, it is a lot of syllables to spit out.

Looking at Tim Matheson's webpage, I found this relevant lesson, which leaves out the first negative. (It also mentions several other equivalent and similar constructions.) I wasn't familiar with this form. If I understand it right, then the corresponding forms with only the latter negative are

I like the interpretation I've seen somewhere on the web, which humorously suggests that the world would end if the condition were not met. It does sound rather ominous if you take the words literally: "If I do not go to the bank, it cannot go." You can also use "narimasen" instead of "ikemasen" with the same meaning, so then it's "If I do not go to the bank, it will not become" -- still ominous.

furrykef wrote:I like the interpretation I've seen somewhere on the web, which humorously suggests that the world would end if the condition were not met. It does sound rather ominous if you take the words literally: "If I do not go to the bank, it cannot go." You can also use "narimasen" instead of "ikemasen" with the same meaning, so then it's "If I do not go to the bank, it will not become" -- still ominous.

two_heads_talking wrote:Unless my memory has escaped me, you could also say.

ginko e ikanakereba narimasen.

Yes, you could! In fact, that's the construction I prefer to use. I don't know why. I guess it was used more often by the people I associated with while I was in Japan. If you break it down, it's quite logical. Literally it says, if I don't go to the bank, it won't happen. i.e. I must go to the bank.

Perhaps some of you are now interested in the difference between narimasen and ikemasen. And I think I’m kind of responsible for clarifying the nuance as a native speaker here. But it’s tough, bluntly speaking. I googled it and the most reasonable explanation I found was that they are almost same and most of the Japanese learners who study it as a second language don’t have to be bothered at least when they are at the intermediate level. Since I know that you won’t be satisfied by that answer, I’ll give it a try.

There are three layers in terms of the difference.

a) 文語的 vs. 口語的Ikemasen sounds more colloquial in many cases.行かなくてはならない （行かなくてはなりません）行かなくてはいけない （行かなくてはいけません）Meaning-wise, roughly speaking, there is no difference between the two. But the latter sounds more colloquial.

b) 義務 vs 責任秘密を教えてはならない秘密を教えてはいけないThe former sounds like there is a strict rule or contract to prohibit it. On the other hand, the latter sounds like it’s only a bad thing to expose the secret.

c) 客観的事実 vs. 主観的判断家賃を払わなくてはならない家賃を払わなくてはいけないThe first is a statement based on an objective fact. But the second has a nuance that the speaker thinks/believes that he must pay it for a subjective reason.

In our actual usage, however, those three nuances are combined in varying proportions so that it’s very hard to tell which should be used in a particular occasion. In that sense, the explanation I found on the internet might be reasonable, I guess.

Great explanation NileCat. That actually clears up some of what I secretly wondered about over the last 2 decades.

I know personally, I used narimasen more often than ikemasen. However, I think I did that because I learned narimasen before I used ikemasen and it was just easier to go to, since it was ingrained earlier in my studies/learning..

NOw, I'd have thought the more colloquial version would be taught, but then, I remembered that as a missionary, it was ok to be 'overly' polite in that you were constantly meeting/contacting people of all ages and to error on the side of politeness was always better than to error on the side of colloquial.

Dear Teachers ~thank you all for your input. Initially, after i went through your posts, i had a follow-up question as to how much value is this "ikana-kutewa-ikemasen" construct.

But i held it off, thinking i should give you all a break.

Thankfully, the answer came by itself as i continued with my little p (as in pimsleur) study. As we were introduced the word, embassy, we had the chance to use it in "i have to go to the embassy." Exact same phrase.

More interestingly for a learner like me, however, is when i was introduced the new word, book a (hotel or, room). That is where the verb changes, but the "have-to" structure which you, my teachers, explained at length for me, paid off.